Creating a Solar Irradiance Logging System Using NI LabVIEW, DAQ, and WSN

"We designed and developed the Solar Irradiance Logging System by integrating NI LabVIEW with NI WSN devices. The system provides a feasible alternative for solar irradiance measurement devices, and we can use the data acquired and logged for analysis and other applications. The system is beneficial for evaluation of solar systems and solar potential of a specific location."

The Challenge:Measuring solar irradiance to evaluate the potential for solar energy at a specific location, deploy solar renewable energy systems, as well as calculate and evaluate the efficiency of solar energy systems. Standard instruments, such as a pyranometer or pyrheliometer, are too costly and not commercially available. We needed to develop an alternative system to measure and log solar irradiance data.

Scientists around the world currently study renewable energy in research and implementation trials. With unlimited availability and renewable features, solar energy is one of the most potential alternative energy resources. Malaysia, located in an equatorial region with abundant year-round sunshine, poses a high potential for applying solar energy systems. To find the best spots for installation, we needed to create a system that measures a location’s solar potential in real time. Our Solar Irradiance Logging System helps ensure that solar energy systems are located in areas for maximum output with maximum efficiency.

Various solar instruments are available to measure solar irradiance; however, they are expensive, which results in the limited use in developed countries. The design and development of our Solar Irradiance Logging System incorporates the measurement and data logging of solar irradiance. The solar irradiance circuit measures the magnitude of irradiance, which transmits across the WSN to LabVIEW for recording and logging.

System Overview

The hardware for our Solar Irradiance Logging System comprises a circuit for acquiring solar irradiance data. LabVIEW reads the data from the DAQ card, and then simultaneously displays and logs the data (see Figure 1). The solar irradiance circuit is the main element of the solar irradiance logging module. The hardware and software interact via WSN and LabVIEW monitors, interfaces, and records the solar irradiance data.

The solar irradiance sensor is a silicon PIN photodiode (BPW34), which is a high-speed and high-sensitive silicon PIN photodiode, sensitive to visible and infrared radiation. A shunt resistance connects in parallel to the silicon PIN photodiode. The resistance suppresses the short circuit current effect in the photodiode, and is adjusted to a critical value which is typically low. In this case, the shunt resistance is 29.9 ohms.

The LM35 precision centigrade temperature sensor is used to measure temperature. A voltage of 5 V powers the device. The sensor’s output voltage is linearly proportional to the Celsius temperature. The temperature value is needed as a correction factor for the solar irradiance measured, which is affected by the temperature of the surroundings when the data is acquired.

The WSN consists of NI WSN-9791 and WSN-3202. The WSN-9791 Ethernet gateway coordinates the wireless network between distributed WSN measurement nodes and the host controller. The WSN-3202 input node functions as a transmitter of the wireless network. The system’s hardware is located outdoors where there is sufficient sunlight, so the design of the enclosure needed to be weatherproof and portable.

The input node is placed inside the project’s portable model, which is then placed at a desired location for installing the solar energy system. Considering the application of solar energy systems, it is possible that the energy systems will be located in remote areas with no place to store the computer that monitors the system. Therefore, we can place the system’s hardware model at a remote location of up to a 300 m outdoor range within line of sight.

Results and Discussion

The GUI’s design applies the classifications of data (see Figure 2). A tab control on the front panel shows data according to the different categories. The first page of the tab control shows the Solar Irradiance Profile, the second page shows the Solar Irradiance Profile with correction factor, the third page shows the Solar Irradiance Profile without correction factor, and the fourth page shows the instantaneous readings. A file directory option at the bottom lets the user specify the directory path for data saving.

Figure 3 shows the program’s block diagram, which consists mainly of three sections: signal conditioning, data logging, and waveform display. The Elapsed Time VI can manipulate the frequency of data acquisition in the program’s block diagram. The VI consists of several main blocks. Two sets of data in the form of voltage are obtained at the input node WSN-3202. Numerical indicators display the respective voltage magnitudes on the front panel. Table 1 defines the scaling factors of the parameters. The temperature signal determines the type of case according to the range of the temperature effect correction factor. The three cases are temperature ranges from 25 to 29, 30 to 39, and 40 to 49 °C. The solar irradiance signal is then multiplied by the respective correction factor according to the different temperature cases. The true solar irradiance values are output from the case structure, displayed on the front panel. LabVIEW plots the solar irradiance data on a waveform graph, which then accumulates to become a solar irradiance profile.

Figures 4 and 5 show the system’s setup. The Ethernet Gateway is connected to the PC where LabVIEW is running to acquire and log data. The input node is located outdoors in a sunny location, placed inside the solar irradiance hardware model.

The project’s experimental results are the data acquisition and data logging of solar irradiance profiles. The results are based on true values obtained from solar radiation during the daytime.

The following are examples of solar irradiance profiles obtained:

1. Profiles on a Sunny Day (Figure 6): Data acquisition time was 8:12 a.m.–5:32 p.m. This set shows a good curve resembling a typical day profile. The sky was occasionally covered by clouds, causing the spikes in the graph as the direct irradiance was blocked by the clouds. However, without the spikes, the profile showed an overall good trend for a location to install solar energy systems. The maximum solar irradiance magnitude was 869 W/m2.

2. Profiles on a Rainy Day (Figure 7): Data acquisition time was 8:35 a.m.–5:05 p.m. This is not an ideal solar irradiance day profile; however, it is useful for comparison with other solar irradiance profiles. Heavy rains and cloudy skies cause the solar irradiance to drop to an average of 58 W/m2. The afternoon sky was still slightly cloudy, so there was little sunshine to raise the irradiance level. The maximum irradiance magnitude achieved was 313 W/m2.

Of the solar irradiance profiles above, at least two show a curve trend of a semicircle-like shape, which is typical for a location with a good profile of solar radiation. In a tropical region such as Malaysia, direct irradiance is much higher than the diffuse irradiance. In locations further from the equator, such as London, the direct irradiance magnitude is not as strong, and the diffuse irradiance plays the more important role in solar radiation.

Conclusion

We designed and developed the Solar Irradiance Logging System by integrating LabVIEW with NI WSN devices. The system provides a feasible alternative for solar irradiance measurement devices. In addition, we can use the data acquired and logged for analysis and other applications. The system is beneficial for evaluating solar systems and the solar potential of a specific location.

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